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Sections 9 .1 – 9.3 Valence Bond Theory Hybrid Orbitals Sigma and Pi Bonding

Sections 9 .1 – 9.3 Valence Bond Theory Hybrid Orbitals Sigma and Pi Bonding. Chemical Bonding Theories. Valence Bond Theory: Uses Lewis Structures Bonds form using shared electrons between overlapping orbitals on adjacent atoms. Orbitals arrange around central atom to avoid each other.

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Sections 9 .1 – 9.3 Valence Bond Theory Hybrid Orbitals Sigma and Pi Bonding

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  1. Sections 9.1 – 9.3Valence Bond TheoryHybrid OrbitalsSigma and Pi Bonding

  2. Chemical Bonding Theories Valence Bond Theory: Uses Lewis Structures Bonds form using shared electrons between overlapping orbitals on adjacent atoms. Orbitals arrange around central atom to avoid each other. Two types of bonds: sigma and pi. Molecular Orbital Theory: Uses MO Diagrams Orbitals on atoms “mix” to make molecular orbtials, which go over 2 or more atoms. Two electrons can be in an orbital. Orbitals are either: bonding, antibonding, or nonbonding. Bonds are either: sigma or pi.

  3. Sigma (s) Bonding Orbitals on bonding atoms overlap directly between bonding atoms Between s orbitals Between s and p orbitals Between p orbitals

  4. Sigma (s) Bonding Consider VSEPR Shapes and bonding:

  5. What’s wrong with this picture? Atoms bond by having their valence orbitals overlap

  6. 2pz 2px 2py 2s Orbitals in CH4 Orbitals on C Orbitals don’t go in same directions as atomic orbitals. Conclusion: Atomic orbitals change shape when they make molecules.

  7. Hybrid Orbitals Atomic valence orbitals “combine and mix” to form new “Hybrid Orbitals” Hybrid orbitals go in the VSEPR electron geometry directions.

  8. Types of Hybrid Orbitals

  9. 4Pairs: sp3 hybrid orbitals

  10. sp3 hybrid orbitals: energetics

  11. sp3 bonding examples

  12. 3 Pairs: sp2 hybrid orbitals

  13. sp2 bonding example: BF3

  14. 2 Pairs: sp hybrid orbitals

  15. sp bonding example: BeF2

  16. More complex example:

  17. Expanded Valence Cases: 5 structural pairs

  18. Expanded Valence Cases: 6 structural pairs

  19. Summary

  20. Bond angles

  21. Sigma vs. Pi Bonding sigma Bonding involves: -- hybrid orbitals -- H 1s orbitals -- terminal atom p orbitals pi bonding involves unhybridized p orbitals

  22. sigma bond formation Orbitals overlap directly between two nuclei:

  23. pi Bond Formation

  24. Bonding in Ethene

  25. Bonding in Acetylene

  26. Advanced: Allene Each end carbon is a flat trigonal. Are they co-planar or perpendicular?

  27. Bonding in Allene

  28. Bonding in Benzene

  29. Summary

  30. Conformations vs. Isomers • Isomers: Molecules with same formula but different structure • Conformers: Different temporary shapes of the same molecule

  31. Bond Rotations • CAN happen around single bonds • Cannot happen around double bonds

  32. cis-trans Isomerization When two groups are on a “side” of a molecule. cis trans

  33. Can these molecules have cis-trans isomers?

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